The present invention relates to the decoding of a sequence of signals. In particular, the present invention relates to the communication of signaling information, such as dual tone multiple frequency (or xe2x80x9cDTMFxe2x80x9d) signals, across a telecommunications network, for example, the public switched telephone network, and the receipt and decoding (or interpretation) of such signaling information.
In telecommunications systems, signaling performs three basic functions; namely (1) supervising functions, (2) alerting functions, and (3) addressing functions. Signaling for supervising functions is used to monitor the status of a transmission line or circuit to determine the state of the line or circuit (i.e., whether it is busy, idle, requesting service, etc.). Voltage levels, tone or data bits for example, are used for supervising function signals. Signaling for alerting functions is used, for example, to indicate the arrival of an incoming call with e.g., bells, buzzers, tones, strobes, lights, etc. Signaling for addressing functions is used to route signals over the network with, for example, dial pulses, tone pulses, and data packets.
Today, most signaling is carried out xe2x80x9cin-bandxe2x80x9d (i.e., it goes along with voice conversations, and occupies the same circuits as those which carry voice conversations). Such in-band signaling is usually carried out with multi-frequency or single frequency signals. Unfortunately, many toll calls are not completed because the called telephone (or other equipment) does not pick up or is busy. Consequently, the circuit time used in signaling, which is substantial and expensive, becomes wasteful. Out-of-band signaling (such as signaling system 7, or xe2x80x9cSS7xe2x80x9d) uses circuit(s) separate from voice circuits for signaling functions.
Although one skilled in the art understands the station equipment and transmission facilities used by Regional Bell Operating Companies (or xe2x80x9cRBOCsxe2x80x9d), a brief overview of such station equipment and transmission facilities is provided below for the reader""s convenience.
FIG. 1 illustrates the use of transmission facilities by various types of services. As shown in FIG. 1, a number of geographically remote central switching offices 120 are coupled via xe2x80x9ctrunksxe2x80x9d 114 and interoffice transmission facilities 118. Various entities, such as residences 102, businesses 104, and private branch exchanges (or xe2x80x9cPBXsxe2x80x9d) 106 are coupled with a central switching office 120 via xe2x80x9clinesxe2x80x9d 110, 112 and xe2x80x9cloop transmission facilitiesxe2x80x9d 108.
Thus, a loop transmission facility (or xe2x80x9csubscriber loopxe2x80x9d) 108 connects telecommunication equipment at a customer premises (e.g., a residence, business, etc.) with an associated central switching office 120. The loop transmission facility 108 is typically on the order of a few miles and usually includes paired copper wire. Interoffice transmission facilities 118, or trunks, connect different central switching offices 120. Interoffice transmission facilities 118 range from less than one mile to thousands of miles.
FIG. 2 is a block diagram showing the connection of two pieces of terminal equipment at customer premises served by separate central offices. Terminal equipment X 202 (such as a telephone or modem for example) is coupled with central office A 206, via loop 208. Similarly, terminal equipment Y 204 is coupled with central office B 210, via loop 212. Central office A 206 is coupled with central office B 210 via trunk lines 214. If all of the trunk lines 214 are busy, central offices A and B, 206 and 210, respectively, may be coupled via trunks 216 and 220 and tandem office C 218.
The flow diagram of FIGS. 3a through 3d illustrates steps involved with initiating a call from terminal equipment X 202 to terminal equipment Y 204, processing the call, and terminating the call, in a system using xe2x80x9cin-bandxe2x80x9d signaling. For the purposes of the following discussion, it will be assumed that the terminal equipment X 202 and Y 204 are telephones. However, the terminal equipment X 202 and Y 204 may be other types of equipment, such as a modem for example.
FIG. 3a shows actions taken at the telephone X 202 and the central office A 206 in initiating the call. First, as shown step 302, when the handset of telephone 202 is lifted, it sends an off-hook signal to the central office A 206 via loop 208. At central office A 206, a change from on-hook to off-hook status is detected. More specifically, when the telephone X 202 is taken off-hook, a circuit is established and the central office A 206 detects a DC current flowing through the established circuit. As shown in step 304, this change in status is interpreted as a request for service. Next, as shown in step 306, assuming that an originating register is available to accept and store the digits to be dialed by telephone X 202, the central office A 206 connects a dial tone signal to the telephone X 202 via loop 208. Line side equipment, such as an analog line unit (or xe2x80x9cALUxe2x80x9d) or an integrated digital carrier unit (or xe2x80x9cIDCUxe2x80x9d) for example, provides the dial tone signal. As shown in step 308 a number is then dialed at telephone X 202. In response, as shown in steps 310 and 312, once the first digit of the number is recognized, the dial tone is disconnected and the numbers are stored in the originating register.
FIG. 3b shows actions taken at the central office A 206 in processing the call. First, as shown in step 314, control equipment at central office A 206 translates the dialed number. The control equipment performs this translation with a dual tone multiple frequency decoder (or DTMF) receiver which is discussed in more detail below. As shown in step 316, by examining the leading digits (e.g., the first three digits) of the dialed number, the control equipment determines whether the call is to another central office (i.e., an xe2x80x9cinter-officexe2x80x9d call) or to a subscriber serviced by the same central office (i.e., an intra-office call). In this example, it is assumed that the call is to telephone Y 204 which is served by a separate central office; namely, central office B 210. Next, as shown in step 318, routing information stored in the system indicates which paths (or xe2x80x9ctrunk groupsxe2x80x9d) are appropriate and translates the desired paths to representations of physical locations of terminations of the trunks. As shown in step 320, if the call is billable, an automatic message accounting (or xe2x80x9cAMAxe2x80x9d) register is requested to enable the telephone service provider to bill the appropriate parties. Next, as shown in step 322, the call information is transferred to an outpulsing register and the originating register is released. Then, as shown in step 324, the control equipment at central office A 206 begins scanning outgoing trunks to find an idle trunk to central office B 210.
If an idle trunk is found, as indicated in step 326, the call be transmitted directly from central office A 206 to central office B 210 via a free trunk 214. If, on the other hand, all trunks 214 from central office A 206 to central office B 210 are busy, then outgoing trunks 216 to tandem switching office C 218 are scanned such that the call may be routed from central office A 206 to central office B 210 via tandem switching office C 218.
FIG. 3c illustrates the actions taken to advance the call to the terminating central office; namely central office B 210. First, as shown in step 328, the idle trunk found in step 326 is seized. In response, as shown in steps 330 and 336, at central office B 210, an incoming register of a switch is seized and control equipment sends a ready signal back to central office A to indicate that the seized incoming register is ready to receive address information. In the meantime, as shown in step 332, at central office A 206, the line of telephone X 202 is connected, via the loop 208 and a switching network within central office A 206, to the seized trunk. In addition, as shown in step 334, control equipment at central office A 206 scans the outgoing trunk for the ready signal.
As shown in steps 338 and 340, when the ready signal sent by central office B 210 is received and detected by central office A 206, the call information is communicated from the outpulsing register of central office A to the seized incoming register of central office B 210. Next, as shown in step 342, before the last digit of the dialed number is sent, the control equipment at central office A 206 checks to see if telephone X 202 is still off-hook. If telephone X 202 is on-hook, the call is abandoned and the control equipment at central office A will terminate the call processing sequence and release associated equipment and circuits (e.g., seized registers, trunks, etc.). If, on the other hand, telephone X 202 is still off-hook, as shown in steps 344 and 346, the last digit of the dialed number is transmitted from the outpulsing register of central office A206 to the incoming register at central office B 210 and the outpulsing register of central office A 206 is released.
FIG. 3d illustrates the actions taken to complete the call. First, as shown in step 350, the digits of the called number stored in the incoming register of the central office B 210 are translated to a physical location of the termination of the loop 212 of telephone Y 204 at central office B 210. Next, as shown in step 352, the status of the loop 212 of telephone Y 204 is checked to determine whether it is idle or busy. If the loop 212 is busy (i.e., telephone Y 204 is off-hook), a busy signal is returned to telephone X 202 via the switching network of central office B 210, trunk 214, the switching network of central office A 206, and loop 208. However, for purposes of this example, it is assumed that the loop 212 of the telephone Y 204 is idle (i.e., telephone Y is on-hook). In such a case, the incoming trunk 214 is coupled with the loop 212 of telephone Y 204 via the switching network of central office B 210. Next, as shown in steps 356, 358, and 360, a ringing register in central office B 210 is seized, the incoming register which stored the dialed number is released, and a ring signal is enabled. The ring is generated by the control equipment. As shown in steps 362 and 364, the ring signal causes an audible ring to be transmitted to telephone X 202 (via the switching network of central office B 210, trunk 214, the switching network of central office A 206, and loop 208) and causes telephone Y 204 to ring (via loop 212). Control equipment at central office B 210 monitors the status of the telephone Y 204. If the handset of the telephone Y 204 is taken off-hook (see step 366) the ringing signal is disabled. The conversation then begins. Further, as shown in step 368, answer supervision, used to record answer or connect time for billable calls, is provided by control equipment at central office A 206.
As shown in step 370, control equipment at central office A 206 monitors the outgoing trunk 214 for disconnect. The call is terminated if either telephone X 202 or telephone Y 204 is hung up, i.e., if its handset is placed on-hook. If the calling party, i.e., telephone X 202, hangs up first, the connection is released (see step 374), and disconnect supervision is sent to central office B 210. The trunk is then idled when central office B returns on-hook supervision. If, on the other hand, the called party, i.e., telephone Y 204, hangs up first, a timed release period of 10 to 11 seconds is initiated. Finally, as shown in steps 372 and 374, upon the expiration of this timed release period, the connection is released.
The above example describes an inter-office call. An intra-office call is handled similarly except that an idle trunk line is not needed. Basically, for intra-office calls, steps 314, 316, 318, 320, 322, 324, 326, 328, 330, 332, 334, 336, 338, 342, 344, and 346 are not performed. Moreover, steps 350, 352, 354, 356, 358, 360, 364, 366, and 372 are all performed at central office A.
To reiterate, the above described flow diagram of FIGS. 3a through 3d illustrates the steps involved with initiating a call from terminal equipment X 202 to terminal equipment Y 204, processing the call, and terminating the call, in a system using xe2x80x9cin-bandxe2x80x9d signaling. Many present day inter-office networks now use out-of-band signaling such as SS7 signaling to xe2x80x9cset upxe2x80x9d (or establish) and xe2x80x9ctear downxe2x80x9d (or terminate) a call. SS7 is used to send messages between remote switching equipment. SS7 is advantageous because it uses separate circuits for signaling and voice data. To reiterate, in the previous systems, the same circuit was used for both signaling and voice data. Such previous systems were disadvantageous because if a circuit was being used for signaling, it could not be used for voice. On the other hand, with SS7, voice trunks are only used when a connection is established.
FIG. 4 illustrates the process of setting up (or establishing) a call 400 in a communications system using SS7. First, as shown in step 402, a caller goes off-hook. Again, the off-hook status of the loop is assumed by the central office based on a DC current through the loop, and the central office returns a dial tone signal to the caller. Next, as shown in step 404, the caller dials digits which causes pulses or DTMF signals to be sent to the central office.
For the purposes of describing the present invention, it will be assumed that the dialed digits will be represented by DTMF signals. As shown in FIG. 5, Each of the digits 0 through 9, as well as the star 11*11 the an the pound sign xe2x80x9c#xe2x80x9d, are represented by a pairing of one of four (4) low frequencies (697, 770, 852, or 941 Hz) with one of three (3) high frequencies (1209, 1336, or 1477 Hz). Since such signaling is xe2x80x9cin-bandxe2x80x9d, and since the frequencies are within the range of human voice, the digits are represented by a paired low and high frequency to avoid having the human voice inadvertently imitating or xe2x80x9cfalsingxe2x80x9d one of the DTMF signals. The amplitudes of the low frequency and high frequency components of the dual tone are also compared with a threshold(s) and each other, to further reduce the chance of falsing.
Next, as shown in step 406, the dialed digits are received and decoded by equipment at the central office. Such equipment may include a standard DTMF decoder such as a model M-8870 DTMF Receiver sold by Teltone. Typically, a DTMF receiver will convert valid dual tonesxe2x80x94i.e., dual tones that: (i) meet a minimum amplitude requirement; (ii) meet a minimum duration requirement (e.g., 18 ms); and (iii) have a minimum interdigit pause (e.g., 18 ms). However, the amplitude, duration and interdigit pauses are not themselves interpreted as carrying any informationxe2x80x94they are only used to determine whether or not a signal is valid.
Next, as shown in step 408, if available, a signaling trunk to the destination office is seized based on a routing table and the decoded dialed digits. As shown in steps 410, 412, and 414, if the dialed equipment is off-hook (i.e., if the line is busy), (i) the destination office signals the central office that the line is busy and (ii) the central office provides busy signal tones to the caller. On the other hand, as shown in steps 410, 416, and 418, if the dialed equipment is not off-hook, (i) the destination office provides ring to the called equipment, (ii) the destination office signals the central office that the line is free, and (iii) the central office provides a ring signal to the caller.
Next, as shown in steps 420 and 422, if the called equipment has gone off-hook, i.e., if the called equipment answers the ring, a connection is established; that is, a voice circuit is seized. If, on the other hand, the called equipment has not gone off-hook, the ringing continues until the attempted call is terminated (not shown) or until the called equipment goes off-hook.
The limited ways of interpreting the twelve dual tone signals limits the information which can be conveyed by a sequence of fixed size (e.g., seven (7) dual tones or ten (10) dual tones). This inherently causes a number of problems, some of which may be classified as line distinction problems, and some of which may be classified as convenience problems.
Regarding the line distinction type problems, as the number of lines used continues to increasing, due to, for example, the increasing prevalence of facsimile machines, modems, home office lines, pagers, etc., area codes are being reformatted. This is disadvantageous because people must remember new area codes and private equipment must be reconfigured to work with the new area codes. For example, some private equipment cannot handle new three (3) digit office codes of the format NNX, where N is a number from 2 to 9 and X is a number from 0 to 9. Such private equipment can only recognize three (3) digit office codes of the format XZX, were Z is either 0 or 1. A similar problem has happened with the limited number of toll-free xe2x80x9c800xe2x80x9d numbersxe2x80x94now, xe2x80x9c888xe2x80x9d is also being used for toll-free numbers. Some private equipment will not recognize 888 as a toll-free number.
Regarding the convenience problems, as the use of facsimile machines, e-mail, modems, pagers, etc. continues to increase, it will become increasingly difficult for people to remember and recall all of those numbers. Although automated touch tone menuing and call forwarding systems have alleviated this problem somewhat, such systems are relatively expensive and require set up time by each end user. Another convenience problem concerns the use of dual tones to enter a security code. On the one hand, if the number of digits entered is too small, the security code would not offer much security and unauthorized access will be made easier. On the other hand, if the number of digits entered is too large, the security code will be difficult to remember thereby possibly preventing authorized people from access or causing authorized people to write down their security number, which may then be lost, copied or stolen. Finally, certain services, such as TeleBroker by Charles Schwab and Co., Inc., require users to xe2x80x9ctypexe2x80x9d letters with their telephone keypad. To xe2x80x9ctypexe2x80x9d a letter, (i) the keypad number to which the letter is assigned is pressed, and (ii) the position of the letter on that number (i.e., first, second, or third) is pressed. FIG. 10 shows a double digit entry to letter conversion table. Unfortunately, such a system requires two entries per letter.
In view of the above, a method and device for interpreting additional information from a sequence of signals, such as dual tone signals for example, is needed.
The present invention obviates the aforementioned problems by providing a method for decoding a sequence of signals to form decoded information. The method (a) determines information from an inherent property of each of the signals of the sequence, (b) determines additional information from a duration of one of the signals and/or an inter-signal pause between two of the signals, and (c) combines the information determined in step (a) and the additional information determined in step (b) to form the decoded information. Each of the signals may be a dual tone signal and the inherent property of each of the signals may be a high and low frequency pair of the dual tone signal. The sequence of signals may be an entered seven digit number.
A central office may use the method of the present invention to route a call based on the decoded information. The call may be routed to a person""s telephone, facsimile, pager, e-mail, voice mail, etc.
The step of determining additional information may be based on a duration of each of at least two, at least three, at least four, at least five, at least six, or all of the signals. Alternatively, the step of determining additional information may be based on durations of inter-signal pauses between three of the signals, four of the signals, or each of the signals.
The present invention also provides a device for decoding a sequence of signals to form decoded information. The device includes (a) a first unit that determines information from an inherent property of each of the signals of the sequence, (b) a second unit that determines additional information from a duration of one of the signals and/or an inter-signal pause between two of the signals, and (c) a combiner that combines the information determined by the first unit and the additional information determined by the second unit to form the decoded information. The first unit may be a dual tone multiple frequency decoder. The second unit may include a timer for determining the duration, and a duration-to-state translator that determines the additional information from the duration.
The method may also be used to decode a signal to form decoded information by (a) determining information from an inherent property of the signal, (b) determining additional information from a duration of the signal, and (c) combining the information determined in step (a) and the additional information determined in step (b) to form the decoded information.